The most widely used method for controlling the temperature of a heat source (linked to a specific power) is to use a closed-loop control in which the temperature of a heat source or its surroundings is determined by a temperature sensor, and in which an automatic control is used to adjust the power of the heat source for the purposes of reaching and maintaining the required temperature. A thermostat may be used for this purpose, for example. Although the closed-loop temperature control is effective, it is not easy to use in some applications, such as cooker hob heat sources.
In devices in which heat sources supplied by external power supplies are used it is desirable that the nominal voltage of the power supply be ascertained, as the heat emitted by the heat sources is directly related to the nominal voltage. Different nominal voltages may thus result in different temperatures in the heat source despite the fact that the required or selected power is the same in all cases.
In the United States, for example, it is known that domestic appliances may be connected to an external 208V three-phase power supply with a phase difference of 120° between two adjacent phases or to a 240V two-phase power supply with a phase difference of 180° between both phases. When a specific power is selected for a determined heat source, the heat emitted by the source may be different if the external supply is 208V or if it is 240V, and it may thus be the case, for example, that food may have to be cooked in a different way in both of these cases.
In order to solve this problem, U.S. Pat. No. 6,841,761 B1 discloses a system for identifying the nominal voltage of the voltage supply to which at least one heat source is connected, which takes into account the phase difference between the various phases of the power supply. The system disclosed in the patent detects the phase difference between two adjacent phases, determining the value of the nominal voltage in accordance with the phase difference detected (if it is 180° the nominal voltage is 240V, and if it is not, it is 208V).